The electron is an elementary particle that carries a negative electric charge. Electrons surround the nucleus in atoms; although contributing less than 0.06% to an atom's total mass, they are responsible of the chemical properties of elements; the exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. Electrons play an essential role in phenomena such as electricity, magnetism, and thermal conductivity.
In the Standard Model of particle physics, the electron is classified in the first generation of the lepton particle family. Its rest mass is approximately equal to 1/1836 of that of the proton.[1] It has a negative electric charge whose magnitude is one elementary charge. It has spin 1/2, meaning that it is a fermion and is subject to the Pauli exclusion principle, according to which no two electrons can occupy the same quantum state. The electron has an anti-particle known as positron, which only differs from the electron in that the electric and other charges have the opposite sign.
Electrons participate in three of the four fundamental interactions of physics: gravitation, electromagnetism, and weak force. Most of the electrons in the universe were created in the Big Bang, but may also be created through beta decay of radioactive isotopes and in high-energy collisions. When an electron collides with a positron, they annihilate into a pair (or more) of photons. During stellar nucleosynthesis electrons are absorbed by protons to form neutrons.
The concept of an indivisible amount of electric charge was first theorized in 1838 by British natural philosopher Richard Laming; the name electron was introduced for this charge in 1894 by Irish physicist George Johnstone Stoney. The electron was identified as a particle in 1897 by J. J. Thomson and his team of British physicists. Other properties of the electron, such as its spin and its wave-like behavior, were determined in the early 20th century. Nowadays, electrons have many applications, including electron beam welding, cathode ray tubes, electron microscopes, radiation therapy, free electron lasers and particle accelerators.